Science-fiction movies have had a long affinity for classical music, and the relationship is a fascinating and complex one. In "Prometheus,"Ridley Scott's quasi-prequel to "Alien," the soundtrack choices are by no means random. Like many sci-fi films before it, "Prometheus" deploys classical music as a kind of cinematic shorthand to signify the presence of a highly evolved intelligence.

The trick is knowing whether that intelligence is benign or malevolent — or perhaps some of both.

One of the movie's recurring images shows a young girl playing the violin. It's the centerpiece of a digital hologram that Weyland Industries has beamed into outer space to demonstrate the achievements of mankind. Like the real-life Voyager probe, which is carrying many classical pieces into space, the hologram is intended to reach intelligent alien life — and to demonstrate our own intelligence and creativity.

In "Prometheus," classical music represents human ingenuity at its best and most ennobling — literally, how we wish to present ourselves to the universe. But the filmmakers also associate classical music with another kind of intelligence — the murderous survivalism of the alien xenomorphs.

[Spoiler alert] The movie concludes with a gruesome bang: the violent birth of a xenomorph, the virulent species that bleeds acid and exists only to kill and propagate itself. The xenomorph utters a deafening scream and then the movie cuts abruptly to Frederic Chopin's Prelude Op. 28, No. 15, which plays over the end credits.

The juxtaposition is jolting, but it's also powerfully suggestive. Here, the movie seems to say, is an organism that is a genetic masterpiece. The aliens, as we know from the previous movies in the series, are supremely intelligent creatures that are capable of outwitting their human adversaries. As the android Ash said in the first "Alien" film, it is the "perfect organism. Its structural perfection is matched only by its hostility."

In the sci-fi genre, Stanley Kubrick's "2001: A Space Odyssey" is ground zero when it comes to the use of classical music. Kubrick scored the movie to Richard Strauss' "Thus Spake Zarathustra" — inspired by the Friedrich Nietzsche book — using its five-note refrain as a musical motif for the evolution of human intelligence . (It should be noted that "Prometheus" contains several references to "2001," as well as to the philosophy of Nietzsche.)

Steven Spielberg's "Close Encounters of the Third Kind" also uses a five-note musical structure to signify a highly evolved intelligence, while Spielberg's "A.I.: Artificial Intelligence" features excerpts from Strauss' opera "Der Rosenkavalier."

The peaceful classical-music coda to "Prometheus" echoes the final credits to "Alien," also directed by Scott. The 1979 movie concluded with Howard Hanson's Symphony No. 2, "Romantic" — a lush orchestral piece that denoted the calm after the death battle between Ripley and the alien.

In both movies, it's a deceptively calm ending. As we now know — and Hollywood has seemingly made sure of it — there is no end to the alien invasion.